The present invention relates to a heterogeneous computer system comprising a host computer and a plurality of I/O subsystems, and more in particular to a method for making it possible to back up the data stored in a memory between a host computer and an I/O subsystem which cannot be directly connected due to the difference in access interface, and a heterogeneous computer system including a plurality of I/O subsystems having different access interfaces connected to the system and the host computer.
In mainframes, a large scale of memory hierarchy (storage hierarchy) including a combination of a plurality of external memories having different processing speeds and different storage capacities is accompanied by a satisfactory data management function and an overall storage management function intended to support an optimum data arrangement and an efficient operation. The IBM's DFSMS (Data Facility Storage Management Subsystem) is an example, which is described in detail in "IBM SYSTEMS JOURNAL", Vol. 28, No. 1, 1989, pp. 77-103.
The disk data of the I/O subsystem of the mainframe computer system having the above-mentioned management function can be backed up in a medium such as a magnetic tape or a magnetic tape library capable of storing a large quantity of data with a low cost per bit.
An open system such as a personal computer or a work station, unlike the mainframe, is not equipped with a magnetic tape or a magnetic tape library capable of storing a large quantity of data.
Generally, in an open system such as a personal computer or a work station, a disk is accessed in accordance with a fixed-length record format, while the mainframe accesses a disk in accordance with a variable-length record format called the count key data format.
As a result, the disk subsystem for the mainframe computer is often configured independently of the disk subsystem for the open system.
On the other hand, a technique for transmitting and receiving data between I/O subsystems is disclosed in U.S. Pat. No. 5,155,845.
In a disk subsystem for an open system and a disk subsystem for a mainframe computer which use different host computers, the back-up and other functions are independently operated and managed.
In view of the fact that the open system lacks a medium such as a magnetic tape or a magnetic tape library capable of storing a larger quantity of data, as described above, it is effective to back up the data in the I/O subsystem of the mainframe.
An ordinary disk system for the open system, however, cannot be connected directly to the mainframe due to the difference in the interface thereof.
U.S. Pat. No. 5,155,845 fails to disclose how to process the read/write operation for a storage system not directly connected to a host computer.